. Discovery. Science. DISCOVERY 159 its physiological effects. Medical heat-baths, in which the patient stands in a cabinet surrounded by a mass of incandescent lamps, have been devised, and the ordinary electric radiator emits almost exclusively rays of this nature. Common experience suggests that the infra-red radiation present in most artificial illuminants has no material prejudicial effect on vision, provided the sources are not brought too near the eyes and- are used discreetly. But continual (_ xposure of the eyes to glowing masses at close quarters is doubtless bad, and the cataract th
. Discovery. Science. DISCOVERY 159 its physiological effects. Medical heat-baths, in which the patient stands in a cabinet surrounded by a mass of incandescent lamps, have been devised, and the ordinary electric radiator emits almost exclusively rays of this nature. Common experience suggests that the infra-red radiation present in most artificial illuminants has no material prejudicial effect on vision, provided the sources are not brought too near the eyes and- are used discreetly. But continual (_ xposure of the eyes to glowing masses at close quarters is doubtless bad, and the cataract that is somewhat prevalent amongst glassworkers and others who work in close proximity to incandescent material has been ascribed to this cause. Much farther down the scale we come to the electro- magnetic waves used in wireless telegraphy and telephony, and between there exists a wide range of infra-red radiations of whose properties little is definitely known. human body furnishes an appreciable amount of heat, instruments which can measure very small quantities of heat could be used to detect the approach of an enemy at night. It is stated that by this device men were easily observed at a distance of 6co feet, and that a person lying on the ground 400 feet away was detected unerringly as soon as he lifted his head above the ground. Thus enemies creeping towards the trenches in the dark could be noted and a warning given. The method is also stated to have found some use in detecting the approach of hostile aircraft, and also as a basis of secret signalling. Experiments on the use of rays at the other extreme end of the spectrum, the ultra-violet, for secret signalling have also been made by the \. Army, and no doubt much work of a similar nature was also done for the British forces. The most striking effects of ultra-violet light are met with in mountainous regions. These rays are V\tra -Violet LIMIT5 OF VISIBLE SPECTRUH ),. "1 r 0 0002 OOOOi 0 0004- 0 0005 0 0006 0 0
Size: 2593px × 963px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcontribu, booksponsoruniversityoftoronto, booksubjectscience
